Noise In Communication System 596g5

NOISE IN COMMUNICATION SYSTEMS Prepared by: Engr. Analene Montesines-Nagayo

NOISE IN COMMUNICATION SYSTEMS NOISE - Any undesirable voltages or currents that ends up appearing in the receiver

output. - Any unwanted form of disturbance of signal or energy tending to interfere with the proper and easy reception and reproduction of desired signal. - Random energy that corrupts and distort the desired signal. - Noise is strong when the signal is weak. - Example of noise in communication system: Noise heard when tuning AM or FM receiver. Hiss or static heard in the speaker. Noise shows up in TV pictures as snow, known as confetti. Noise that occurs in the transmission of digital data manifest itself as bit error. Signal loss

NOISE IN COMMUNICATION SYSTEMS Noise can affect the communication system performance in three areas: Noise can cause listener to misunderstand the original signal or be unable to understand it at all. Noise can cause the receiver to malfunction. Noise can cause the receiver’s circuitry to function incorrectly, erratically or improperly. Noise can also result in a less efficient system.

NOISE IN COMMUNICATION SYSTEMS Noise can be divided into two general categories: A. UNCORRELATED NOISE  noise present regardless of whether there is a signal present or not. B. CORRELATED NOISE  noise present as a direct result of a signal.  mutually related to the signal and cannot be present in circuit unless there is an input signal and is produced by non-linear amplification.  No signal, no noise.

NOISE IN COMMUNICATION SYSTEMS TYPES OF UNCORRELATED NOISE 1. EXTERNAL NOISE • Noise present in the received radio signal that has been introduced in the communication medium. • Noise generated outside the device or outside the receiver. 2. INTERNAL NOISE • Noise produced by active and ive devices in the receiver. • Noise generated within the device or within the receiver.

NOISE IN COMMUNICATION SYSTEMS TYPES OF EXTERNAL NOISE 1. MAN-MADE / INDUSTRIAL NOISE  produced by spark-producing mechanism such as commutators in electric motors, automobile ignition system, power switching equipment, fluorescent and gas filled lamps.  produced by any equipment that causes high voltages or currents to be abruptly switched. This noise is called impulse noise.  Noise in DC power supply such as AC ripple.  Noise in AC power line such as surges of currents and voltage.  Noise introduced by nearby communication system.  In general, Man-made/Industrial noise are form of electromagnetic interference that can be traces to non-natural causes.  Industrial noise frequency is between 15 to 160MHz, and it can extend to 500MHz.

NOISE IN COMMUNICATION SYSTEMS 2. ATMOSPHERIC NOISE - Noise caused by naturally occurring disturbances in the Earth’s atmosphere, such as static caused by lightning and thunderstorm. - It has a great impact on signals at frequencies less than 30MHz.  Form of interference caused by rain, hail or snow is called precipitation static.

NOISE IN COMMUNICATION SYSTEMS 3. EXTRATERRESTIAL / SPACE NOISE Noise coming from outer space due to sun, stars, distant planet and other celestial bodies. Noise caused by the sun is called solar noise. It is cyclical and reaches a very annoying peak every 11 years. Noise caused by stars, distant planet and other celestial objects is called cosmic noise. It has great impact on signals with frequencies beginning at approximately 8 MHz and extends out to 1.43 GHz and beyond.

NOISE IN COMMUNICATION SYSTEMS TYPES OF INTERNAL NOISE 1. THERMAL AGITATION/ WHITE/ JOHNSON NOISE  Noise generated in any power dissipating component in the circuit such as resistor.  Thermal agitation refers to the rapid and random motion of electrons in an electronic component caused by heat.  As temperature increases, increasing number of electrons moves through the component, causing small noise voltage to be produced across the component.

NOISE IN COMMUNICATION SYSTEMS TYPES OF INTERNAL NOISE 2.

SHOT NOISE  Shot noise is produced by random movement of electrons or holes across a PN junction due to discontinuities.  Noise due to the random arrival of charge carriers (electrons or holes) at the output element of an active electronic device such as diode, transistor and vacuum tube.

NOISE IN COMMUNICATION SYSTEMS TYPES OF INTERNAL NOISE

3. TRANSIT TIME NOISE  High frequency noise caused by transistor and vacuum tubes due to delayed movement of current carriers (electron or holes) from input to output terminal of the device (such as from emitter to collector of a transistor).  - Shows up as a kind of random noise within the device and is directly proportional to the frequency of operation.

NOISE IN COMMUNICATION SYSTEMS TYPES OF INTERNAL NOISE 4. EXCESS/

PINK/FLICKER NOISE  Noise caused by transistor and vacuum tubes due to crystal surface defects.  Low frequency noise (below 1KHz.) from carrier density fluctuations. It is proportional to emitter current and junction temperature, inversely proportional to frequency.

5. MIXER NOISE  Noise caused by low transconductance of mixer compared to amplifiers and inadequate image frequency rejection.

NOISE IN COMMUNICATION SYSTEMS TYPES OF INTERNAL NOISE 6.

GENERATION-RECOMBINATION NOISE  Noise caused by random fluctuation of semiconductor conductivity giving rise to noise current when DC signal flows through the semiconductor.

7. CROSSTALK  Interference signal from one channel to another.

NOISE IN COMMUNICATION SYSTEMS TYPES OF CORRELATED NOISE 1. HARMONIC DISTORTION  Unwanted multiples of a single frequency sine wave that are created when sine wave is amplified in a non-linear device, such as large signal amplifier. 2. INTERMODULATION INTERFERENCE  Unwanted cross-product (sum & difference) frequencies created when two or more signals are amplified in nonlinear device.

NOISE IN COMMUNICATION SYSTEMS NOISE CALCULATIONS

NOISE POWER, Pn in Watts (W) PN = K T B where : K = Boltzman’s constant , 1.38 x 10–23 J/K T = absolute temperature in K B = frequency bandwidth in Hz

PN PN (dBm)  10 log 3 1x10

NOISE IN COMMUNICATION SYSTEMS NOISE POWER DENSITY / POWER SPECTRUM DENSITY, No units: in Watts/Hertz (W/Hz) average noise power / bandwidth a figure that determines the amount of noise contained in a specified bandwidth

PN No   KT B No No(dBm )  10 log 1x10 3

NOISE IN COMMUNICATION SYSTEMS NOISE VOLTAGE, VN in Vrms

VN  4KTBR where : K = Boltzman’s constant , 1.38 x 10–23 J/K T = absolute temperature in K B = frequency bandwidth in Hz R = equivalent noise resistance in W

NOISE IN COMMUNICATION SYSTEMS RMS NOISE VOLTAGE DUE TO SEVERAL SOURCES For series combination,

VNT 

VN 1  VN 2  VN 3 2

2

2

RNT  RN 1  RN 2  RN 3 For parallel combination,

VNT 

VN 1  VN 2  VN 3

RNT 

1 1 1   RN 2 RN 3

2

1 RN 1

2

2

NOISE IN COMMUNICATION SYSTEMS SHOT NOISE CURRENT, iN in Amperes (A) rms A form of internal noise which is due to the random variations in current flow in active devices such as diode,transistor and vacuum tubes.

iN  2 q IB where : q = electron charge =1.6 x 10–19 C B = frequency bandwidth in Hz I= DC bias current of the device in Amperes

NOISE IN COMMUNICATION SYSTEMS SIGNAL TO NOISE RATIO, SNR  shows how much stronger or weaker the desired signal power is compared to the unwanted noise.  indicates how easy or difficult it will be to extract the desired information from corrupting noise. SNR as power ratio:

SNR as voltage ratio:

signal power (Ps) (Ps) signal power SNR  SNR noise power (Pn) noise power (Pn) Ps SNR in dB  10 log Ps Pn SNR in dB  10 log

 signal voltage (Vs)   SNR    noise voltage (Vn) 

Pn

SNR in dB  20 log

Vs Vn

2

NOISE IN COMMUNICATION SYSTEMS NOISE FIGURE (NF) / NOISE FACTOR (F) shows exactly how much of noise in the amplified signal is due to the original signal and its noise, compared to the noise added by the amplifier itself. shows how much noise is added to the received signal by the noise of the circuitry itself.

SNRi F  SNRo SNRi NF (dB)  10 log  10 log F SNRo NF (dB)  SNRi (dB)  SNRo (dB)

NOISE IN COMMUNICATION SYSTEMS NOISE FIGURE OF IDEAL NOISELESS AMPLIFIER F = 1 and NF (dB) = 0 dB

NOISE FIGURE OF AMPLIFIER WITH INTERNALLY GENERATED NOISE F>1

NOISE IN COMMUNICATION SYSTEMS REACTANCE NOISE EFFECTS The significant effect of reactive circuits on noise is their limititaion on frequency response The equivalent bandwidth to be used in noise calculations with reactive circuits is

 Beq  B3dB 2

where : B3dB = half power bandwidth, Hz Beq = effective bandwidth, Hz

NOISE IN COMMUNICATION SYSTEMS EQUIVALENT NOISE TEMPERATURE, NT or Teq in K NT = Teq = To (F – 1) where : F = noise factor To = reference absolute temperature, 290 K

NOISE IN COMMUNICATION SYSTEMS NOISE DUE TO AMPLIFIERS IN CASCADE

Friss formula Over-all noise factor of n stages

Feq

Fn  1 F2  1 F3  1  F1    ...  G1 G1G2 G1G2 ..Gn 1

Over-all noise temperature of n stages

Teq

T3 Tn T2  T1    ...  G1 G1G2 G1G2 ..Gn1 where: G is the power gain

NOISE IN COMMUNICATION SYSTEMS NOISE DUE TO AMPLIFIERS IN CASCADE

Friss formula Over-all noise resistance

R eq

R3 Rn R2  R1  2  2 2  ...  2 2 2 A1 A1 A2 A1 A2 ... An1 where: A is the voltage gain

NOISE IN COMMUNICATION SYSTEMS Example #1. A receiver has a 50W input resistance, a bandwidth of 2 MHz, and a temperature of 30oC.

1.1 The noise power is ___________W. (a) 8.26x10-16

(b) 8.36x10-15

(c) 2.76x10-17

(d) 1.29x10-6

1.2 The thermal noise voltage is ______ Vrms. (a) 3.35x10-14

(b) 1.67x10-12

(c) 4.18x10-11 (d) 1.29x10-6

1.3 The noise density in dBm is ______. (a)–203.79

(b) -173.79

(c) –347.57

(d) –407.57

Example #2. What is the noise temperature when the noise power is 12 x 10-18 W and the bandwidth is 3KHz? (a) 289.86 K (b) 16.86 K

(c) 273 K

(d) 0K

NOISE IN COMMUNICATION SYSTEMS Example #3. What is the noise resistance when the noise voltage is 1.15mV with a bandwidth of 800KHz and a temperature of 29oC? (a) 898M W

(b) 99.17M W

(c) 86.23MW

(d) 1.03K W

Example #4. A noiseless amplifier having a gain of 60, a bandwidth of 20MHz and an operating temperature of 40oC amplify the noise voltage generated by a resistor. The output noise voltage is measured as 1mVrms. 4.1 The rms input noise voltage is ______. (a) 60mV

(b) 1 mV

(c) 23.57 mV

(d) 16.67mV

4.2 The noise resistance is _______. (a) 10.42G W (b) 2.89MW

(c) 804.19 W

(d) 1.61K W

NOISE IN COMMUNICATION SYSTEMS Example #5. What is the SNR in dB for signal power of 50W and a noise power of 0.1 W? (a) 50 dB

(b) –26.99 dB (c) 26.99 dB

(d) 53.98 dB

Example #6. What is the noise figure in dB when the input signal and noise values are 1W and 0.01W, and the output signal and noise values are 10W and 0.1W? (a) 0 dB

(b) 100 dB

(c) 1 dB

(d) 10 dB

Example # 7. Two resistor, 20KW and 50KW, are at ambient temperature. Calculate for a bandwidth equal to 100KHz, the thermal noise voltage for the two resistors connected in parallel. (ECE Board, November 1997) (a) 4.28mV

(b) 47.8 mV

(c) 4.78 mV

(d) 0.48mV

NOISE IN COMMUNICATION SYSTEMS Example # 8. What is the signal to noise ratio at the output of the amplifier in dB when the input signal and noise values are 0.1 x 10– 3 V and 0.01 x 10-6 V respectively? The amplifier’s voltage gain and internal noise voltage are 1000 and 1 x 10-5 V respectively. (a) 80 dB

(b) 74 dB

(c) 34 dB

(d) 40 dB

Example # 9. What is the equivalent noise temperature for a totally noiseless amplifier? (a) 290 K

(b) 17oC

(c) 30oC

(d) 0K

Example # 10. Determine the shot noise current for a diode with a forward bias current of 1mA over a 100KHz bandwidth. (a) 3.2x10-17A

(b) 5.66nA

(c) 4nA

(d) 8nA

REFERENCES  Electronic Communication Systems Through Advanced by W. Tomasi  Communication Electronics by L. Frenzel  Lecture Notes in Principles of Communication by A.H. Ballado and M.M. Sejera  Electronic Communication Systems by G. Kennedy